The present invention relates to a vacuum arc evaporation source and a vacuum arc vapor deposition apparatus provided with the vacuum arc evaporation source.
A vacuum arc vapor deposition apparatus has been heretofore known in which an arc discharge with an evaporation material being a cathode is generated in a vacuum chamber, and a cathode material is evaporated and ionized by energy of an arc current to accumulate films on a substrate.
Such a vacuum arc evaporation apparatus has a disadvantage that molten particles having a diameter in excess of a few xcexcm which is far larger than that of evaporated particles and ionized particles are unavoidably generated, which are mixed into films, resulting in deterioration of coarseness of film surface and unevenness of film composition.
There has been proposed to solve such a problem caused by the molten particles as described above by generation of a magnetic field. For example, in Japanese Patent Application Laid-Open No. 2-194167 Publication is disclosed that an air-core coil coaxial with an evaporation surface is provided between the evaporation surface and a substrate. According to the constitution disclosed therein, electrons in a plasma are wound around the line of magnetic force caused by the air-core coil and flow along the line of magnetic force while performing a turning movement so that the plasma arrives at the substrate. On the other hand, the aforesaid induction effect does not act on neutral molten particles, and ions are selectively guided to the substrate, because of which the number of molten particles relatively moving toward the substrate cannot be reduced.
However, in the case of the aforementioned technique, the coil is provided in an intermediate position between the substrate and the evaporation surface, and the magnetic field caused by the coil acts so as to move inwardly in the radial direction of the evaporation surface. In this case, an arc spot tends to move closer to the center of the evaporation surface, and the evaporation materials are not consumed uniformly. Furthermore, where a plurality of evaporation sources are provided in a vacuum container, there is an undesirable influence from other evaporation sources since the magnetic field is extensive.
The present invention has been accomplished in view of circumstances as described above. It is an object of the present invention to provide an evaporation source capable of reducing the number of molten particles arriving at a substrate by a magnetic field, and capable of reducing the unbalance of occurrence of arc spots.
For achieving the aforementioned object, the present invention has taken the following technical means. That is, the feature of a vacuum arc evaporation source according to the present invention, lies in the provision of an evaporation material as a cathode of arc discharge, and a magnetic field generating source arranged so that a magnetic field generating source surrounds the evaporation material, and all the lines of magnetic force crossing the evaporation surface of the evaporation material crosses substantially vertically to the evaporation surface.
According to the constitution as mentioned above, molten particles can be reduced similar to the prior art by the lines of magnetic force crossing the evaporation surface. Since the lines of magnetic force substantially vertically cross the evaporation surface, unlike the prior art, the arc spot is hard to be deviated on the evaporation surface, and the evaporation material is uniformly consumed.
The lines of magnetic force need not cross the evaporation surface completely vertically, but may cross the evaporation surface substantially vertically. The substantially vertical termed in the present invention indicates within xc2x130 degrees with respect to normal line of the evaporation surface. If in the range as described, this is within an allowable range capable of achieving uniform consumption of the evaporation material to some extent. Accordingly, the magnetic field generating source may be arranged at a position so that the lines of magnetic force assume a direction as described.
Preferably, the magnetic field generating source is arranged so that the direction of the lines of magnetic force in the evaporation surface is within xc2x110 degrees with respect to normal line of the evaporation surface. In this case, the evaporation material can be consumed more uniformly.
The magnetic force generating source according to the present invention may be a permanent magnet, an electromagnet or coil wound around the outer periphery of the evaporation material. Preferably, a permanent magnet is used as a magnetic field generating source in view of miniaturization of apparatus.
As the specific constitution of a magnetic field generating source for causing lines of magnetic force to cross the evaporation surface substantially vertically, suitably, the magnetic field generating source is arranged so that the evaporation surface is positioned at an intermediate position between both N and S poles of the magnetic field generating source.
The intermediate position between both the N and S poles need not be central between both the magnetic poles. However, if the magnetic field generating source is arranged so that the evaporation surface is positioned at substantially central position between both the N and S poles, the direction of the lines of magnetic force further tends to register with the normal direction of the evaporation surface, which more suitable.
Preferably, the magnet comprises an in-diametral magnetic field generating source surrounding the evaporation material, an out-diametral magnetic field generating source surrounding the in-diametral magnetic field generating source so that the same axial and same pole as the in-diametral magnetic field generating source are directed in the same direction. In this case, the number of lines of magnetic force extending through the evaporation material increases, that is, the intensity of magnetic field becomes high to obtain the aforementioned effect more strongly.
Further, according to the present invention, the magnetic force generating source may comprise a first magnetic field generating source having magnetic poles on the inner peripheral side and on the outer peripheral side, and a second magnetic field generating source in which magnetic poles on the inner peripheral side and on the outer peripheral side are different from those of the first magnetic field generating source and arranged in an axial direction of the first magnetic field generating source.
According to the constitution as described above, extension of the magnetic field generating source in an axial direction is small, which is preferable. In this case, if the outer peripheral sides of the first magnetic field generating source and the second magnetic field generating source are connected by a magnetic material, extension of the magnetic field sideward is rarely present, and so, where a plurality of evaporation sources according to the present invention are provided in a vacuum container, an influence of next evaporation source can be eliminated.
Further, for obtaining the similar effect, the magnetic field generating source may be constituted as a permanent magnet having a U-shape in section having both N and S magnetic poles on the in-diametral side.
In the more preferable constitution according to the present invention, there comprises the magnetic material surrounding the outer periphery of the evaporation material. The magnetic material draws the lines of magnetic force and consequently lines of magnetic force formed by this magnetic field generating sources are inclined somewhat in the outer peripheral direction. An arc has character that the arc tends to move in an inclining direction of lines of magnetic force, in which case, an arc spot is affected by the lines of magnetic force inclined in the outer circumferential direction, and moves in the outer circumferential direction. Thereby, the arc spot approached the outer peripheral portion of the evaporation surface is pushed back to the center of the evaporation surface to obtain a further stronger arc confining effect.
Preferably, between the evaporation material and the magnetic material is provided an insulator for electrically insulating both the materials. When the magnetic material is not insulated from the evaporation surface and both have the same potential, there is the possibility that the arc spot moves from the evaporation surface to the magnetic material, which can be, however, prevented passively by the provision of the insulator.
As the insulator, an insulating material can be interposed between the outer periphery of the evaporation material and the inner periphery of the magnetic material, but the insulator preferably comprises a clearance capable of insulating the evaporation material and the magnetic material. When as the insulator, a member (an insulating element) is provided between the evaporation material and the magnetic material, the evaporation material is evaporated and adhered to the member, resulting in a possible occurrence of inferior insulation. However, if the insulator is constituted as a clearance, such a possible adhesion disappears and the inferior insulation is prevented.
More preferably, a direction changing means for changing lines of magnetic force to a direction inclined on the peripheral edge with respect to normal line formed on the evaporation surface is provided in the vicinity of a central portion of the evaporation material. Thereby, concentration of arc on the central portion of the evaporation surface is prevented, resulting in uniform consumption.
Means for imparting a change to a direction of lines of magnetic force from the magnetic field generating source that can be employed includes a magnet, a coil or a magnetic material. When the magnet, the coil or the magnetic material is arranged on the back side of the central portion of the evaporation material, the lines of magnetic force in the vicinity of the center are drawn to the magnet, the coil or the magnetic material, whereby the lines of magnetic force in the vicinity of the center are inclined outward with respect to normal line. When the central lines of magnetic force are inclined outward, concentration of arcs on the central portion of the evaporation surface is prevented, due to the characteristic that the arc tends to move in the inclining direction of lines of magnetic force, and uniform consumption results.
A horizontal magnetic force component is generated on the evaporation surface by inclination of lines of magnetic force whereby the arc spot rotates, but its region is enlarged so that inclination is large to make it possible to make the moving rate of the arc spot high in a wide range, as a consequence of which a local rise in temperature of the evaporation material is suppressed and occurrence of droplets reduces. Further, when a magnet or a coil is used as the line of magnetic force direction changing means, magnetic flux density becomes high, thus making it possible to make the moving rate of the arc spot high, and to further prevent higher temperature.
According to the vacuum vapor deposition apparatus in which the evaporation source is provided in the vacuum container, an accidental fire of arc can be prevented to provide efficient operation, and reduction in droplets enables formation of films of high quantity.